The invention relates to a disengageable cylinder for an automobile lock mechanism.
The addition of a disengageable mechanism to a cylinder intended for an automobile lock makes it possible to prevent this cylinder from being forced. Specifically, if an improper key, or any other flat tool of suitable shape, is inserted into the rotor, and if an attempt is then made to rotate the rotor, the disengagement mechanism enables the rotor and the intermediate sleeve to pivot freely inside the stator without considerable stresses being exerted on the tumblers.
The fact is that, in the presence of excessive stresses, the tumblers are liable to be damaged or be retracted by force, thus allowing the cylinder to be unlocked without the appropriate key.
The invention is concerned more precisely with a disengageable cylinder, in particular for a motor vehicle lock mechanism, comprising a fixed stator, a tubular intermediate sleeve which is mounted in rotation about its axis in the stator and which is fixed axially with respect to the stator, a rotor which is mounted in rotation in the sleeve, which is fixed axially in the sleeve and which comprises tumblers which can move radially under the action of a key intended to be inserted axially into the rotor. Tumblers are fully retracted inside the rotor when the key is appropriate, so as to allow a free rotation of the rotor with respect to the sleeve and the stator and thus allow a lock operating lever, called a cam actuator, to be rotated, this lever being coupled to the rotor via a driver. The rotor and the intermediate sleeve are blocked against rotation with respect to one another by the tumblers when the key is not appropriate. The cylinder also comprises an indexer which can move axially between a rest position and a disengagement position, under the effect of a rotation of the sleeve with respect to the stator subsequent to the rotor being rotated by means of an inappropriate key, so as to move the driver axially toward a disengaged position.
In such a known cylinder, as the disengagement is taking place, more precisely at the start of the movement of the various parts to achieve this disengagement, the cam actuator is caused to rotate out of its rest position, called 0° position, corresponding to the locking of the lock, because of displacements between the relative movements of the various parts, particularly the driver and the indexer. This rotation generally occurs over 15° more or less. This rotation causes a movement of the linkages of the locking system which is connected to the lock.
This residual rotation is problematic since, taking account of the maximum rotational movement of the cam actuator from the locked position to the unlocked position, which may be relatively small, it may result in an unintentional opening of the door or flap bearing the cylinder.
The invention solves this problem by providing a disengageable cylinder which ensures that the cam actuator is automatically returned to the rest position immediately following this residual rotation, while at the same time making available a particularly compact cylinder, that is to say one with a limited length and particularly robust construction.